DATA UPDATE SYSTEM, DIFFERENTIAL DATA CREATING DEVICE AND PROGRAM FOR DATA UPDATE SYSTEM, UPDATED FILE RESTORING DEVICE AND PROGRAM

摘要

A data update system in which the amount of differential data used for data update is reduced. When differential data is created, Move/Add determining means (35) determines which is created, Move data or Add data. The Move data represents a Move instruction to move and copy data from an unupdated file to an updated file, and the Add data represents an Add instruction to add data and copy it. For the determination, agreeing data sequence searching means (34) searches for data in the unupdated file agreeing with that in the updated file. When the length of data sequence to be copied is 5 byte or more, Move data output means (36) outputs the data sequence as Move data; contrarily when the length is 4 byte or less, Add data output means (37) outputs it as Add data. By combining the Move data with the Add data, differential data is created. The Move size and Move address of the Move data are expressed by using variable length bits. Thus, the amount of differential data is reduced.